Hi Dumitru. I found out that assemply numbering is not the problem. The problem is asimetrical parts. When you will mirror some asymetrical part like L-shape or C-Shape (see picture C-Shape = U-Shape) then the exactly same elements wits same features get diferent part number, because of this parts same assemblyes gets different asembly numbers. (on attached picture i make 4 profiles, I, C(U), L and SHS and drill 2 holes) the I and SHS shapes gets same numbers but L and C profiles gets different numbers. Best regards and Happy New Year.